The present invention relates to one-phase liquid cleansing compositions having enhanced antimicrobial effectiveness. More specifically, the invention relates to a hydroxy acid compound or compounds, more particularly lactic acid which potentiate the antibacterial activity of liquid cleaning formulations by buffering the pH of the formulation such that the pH will rise no higher than 5.0, preferably between 2.5 to 5.0 under in use conditions (as opposed to initial pH).
There is a large demand in the market for mild liquid cleansing formulations which additionally have an antibacterial effect. Antibacterial cleansers are preferred because they kill germs and mild personal cleansers are preferred to minimize skin irritation, dryness, etc. However, the combination of mild cleansing formulations and strong antibacterial effect is difficult to achieve. Thus, for example, while soaps provide antibacterial effects, they are not mild to the skin. When very mild non-soap surfactants are used, antibacterial effect is greatly compromised.
The balancing act between providing mildness and effective antibacterial effectiveness is recognized for example in International Publication WO 92/18100. In this publication, improved clinical mildness is said to be provided through the use of a water soluble cationic polymer (see page 10, lines 24-29). Cationic polymer is apparently used instead of additional ethoxylated surfactant because the percent of ethoxylated mildness surfactant must be minimized in order not to affect antibacterial effectiveness (page 7, lines 4-6).
Another approach to providing mildness effect without affecting antibacterial properties is that which appears to be used by Dial in, for example, Liquid Dial Plus with Moisturizers Antibacterial Soap.RTM.. Here, mildness benefits are apparently provided by the use of moisturizing compounds rather than by the use of very mild surfactants alone (which, as indicated above, compromises antibacterial effectiveness).
In both cases, it can be readily seen that it is extremely difficult to provide effective antibacterial action in the presence of very mild surfactants, to use larger amounts of harsher surfactants or soaps and to mask the effects of the harshness by providing cationic mildness conditioning agents (WO 92/18100) or moisturizers (as in the Dial product).
It would be greatly beneficial if antibacterial effectiveness could be provided either by providing a compound or compounds which alone or together buffer pH of a liquid composition at a pH low enough to provide antibacterial effectiveness for that composition formulation (while maintaining stability of composition); or by providing a compound or compounds which alone or together buffer pH of a liquid composition containing anti-bacterial agent thereby enhancing (i.e., potentiating) the effect of the antibacterial agent even in compositions with very mild surfactant systems.
Fatty acids and their ester derivatives have been used to provide antimicrobial effectiveness in foods, pharmaceuticals and cosmetics (see, for example EP 0,244,144; U.S. Pat. No. 4,002,775; U.S. Pat. No. 4,406,884; U.S. Pat. No. 4,997,851 and Kabara in JAOCS, vol. 61, No. 2, (February, 1984)).
The use of short chain fatty acids generally as potentiators of germicides is also known. These fatty acids, for example, have been used as potentiators with halogenated germicides at high pH and with isethiazolones (see FR 2,223,049 and EP 488,606).
U.S. Pat. No. 3,218,260 to Lewandowski discloses cleaner compositions containing various organic or inorganic acids. The pH of these compositions (less than 2) is well below the pH of the skin cleansing compositions of the present invention.
In none of these references is it taught or suggested that one or more compounds be used either to enhance antibacterial effect in liquid skin cleansing compositions or to potentiate antibacterial compounds which may already be present in liquid skin cleansing compositions at the pH specified by the claims of the subject invention.
Further, none of these references relate to use of hydroxy carboxylic acid (e.g., lactic acid).
U.S. Pat. No. 5,132,037 to Greene et al. teaches aqueous compositions in which C.sub.8 -C.sub.22 free fatty acids may be used. All examples (palmitic, stearic) are clearly directed to longer chain fatty acids and there is absolutely no recognition of the antibacterial or potentiating effect of lower chain fatty acids. Also, there is no teaching or suggestion of hydroxy carboxylic acids.
U.S. Pat. No. 5,137,715 to Hoshowski et al. teaches shampoo conditioner compositions wherein the pH of the composition can be in the range of 2.5 to 7.0. The invention requires a polymeric amidoamine compound (substantive compound which imparts conditioning and does not adversely affect foam of anionic; see column 11, line 63 to column 12, line 36). It is further taught that an acid is required to neutralize the amidoamine and one acid which is said to be used for this purpose is citric acid (see column 13, lines 49-65).
The compositions of Hoshowski, while stable, were only stable when using the specific amidoamine of formula I (Example 13 of the patent notes that an extremely similar amidoamine, represented by Formula V, caused instability at pH below 6.0) and, according to examples, 2% citric acid was used.
In general Hoshowski et al. makes clear that most amidoamines would cause instability. More specifically, applicants tried the amidoamine of Formula I in compositions of the subject invention and also found instability. Applicants are not certain whether this instability was due to large amounts of hydroxy acid (applicants use minimum 0.5% lactic acid versus 0.2% citric acid exemplified); whether it was due to the specific hydroxy acid used; or whether it was due to the specific surfactant system. What is clear, however, is that there is no such instability in the system of the invention without the amidoamine of Formula I while there is such instability using the amidoamine in the same system.
U.S. Pat. No. 5,002,680 to Schmidt et al. teach skin cleansing aerosol mousse emulsions comprising:
(A) 88% to 97% of a concentrate comprising: PA1 (B) 3% to 12% propellant. PA1 (1) enhance the antibacterial effect of liquid skin cleansing compositions; and/or PA1 (2) potentiate antimicrobial effect of liquid skin cleansing compositions which already contain an antimicrobial agent. PA1 (1) any mild surfactant system (i.e., any one or more surfactants which alone or together are demonstrated by clinical tests to be milder than soap itself) in an amount of from about 1-99% by wt., preferably 2-85% by wt., more preferably 3-40% by wt. surfactant system; PA1 (2) 0.5 to about 9%, preferably 0.5 to 5% by weight of a hydroxy carboxylic compound or compounds (e.g., lactic acid) which alone or together buffer the pH of the liquid skin cleanser composition such that the pH is no higher than 5.5 under in-use conditions (i.e., 1:0.5 to 1:100 dilution, preferably 1:1 to 1:25 dilution of product in H.sub.2 O); and PA1 (3) 1% to 99% by wt., preferably 15 to 97%, most preferably 60 to 97% by wt. water. PA1 (1) 1% to 99% by wt. of surfactant system comprising: PA1 (2) 0.5 to 9% hydroxy acid; and PA1 (3) 1% to 99% water.
(1) 3%-20% anionic or amphoteric; PA2 (2) 0.05 to 5% polymeric skin feel aid; PA2 (3) 10% to 60% moisturizers (which can be lactic acid); and PA2 (4) water; and PA2 (a) 1 to 30% by wt. of at least one anionic surfactant; PA2 (b) 0.5% to 15% amphoteric surfactant;
This reference differs from the subject compositions in a number of ways. First the lactic acid, if used, is used as moisturizing component and must comprise 10% or greater of composition whereas upper level of the hydroxy carboxylic acid of invention (to provide bactericidal effect) is about 9%. Further, the reference is not a single phase composition but comprises propellant (to form mousse). While not wishing to be bound by theory, bactericidal effect of hydroxy acid of invention are believed to be due largely to single phase systems of invention. In a multiphase, it is believed surfactant would not have time to solubilize and enter liquid phase and therefore could not deliver antibacterial activity.
In short, applicants have now found that one or more hydroxy compounds may be used to buffer low pH within a defined low pH range and to therefore:
The single phase compositions of the invention are free of amidoamines generally and more specifically, of the amidoamines described in U.S. Pat. No. 5,137,715 to Hoshowski.